As is well known to those skilled in the art, middle distillate hydrocarbons and lubricating oils are commonly employed under conditions wherein their oxidation stability is a significant factor. In the case of lubricating oils for example the properties of the oil may be significantly changed when the oil is subjected to oxidation. Typically the oil may become darker, thicker, and it may decompose to a mixture containing a larger concentration of solids. When the lubricating oil contains additives such as viscosity index improvers for example, it is found that many of these additives are particularly susceptible to oxidation; and their effectivity is diminished as they are oxidized during operation.
It is an object of this invention to provide an anti-oxidant system which is particularly characterized by its ability to function in hydrocarbon oils. Other objects will be apparent to those skilled in the art.